Causes

The precise causes of psoriasis are unknown. It is generally believed that psoriasis is a disorder in which factors in the immune system, enzymes, and other biochemical substances that regulate skin cell division become impaired. This abnormal immune response causes rapid proliferation of keratinocytes (immature skin cells) and inflammation. Such events are likely to be triggered by environmental factors, such as weather or stress, in people with genetic factors that make them susceptible.

Inflammatory Response and Autoimmunity

The Normal Immune System Response. The inflammatory process is a byproduct of the body's immune system, which fights infection and heals wounds and injuries:

• When an injury or an infection occurs, white blood cells are mobilized to rid the body of any foreign invaders, such as bacteria or viruses.
• The masses of blood cells that gather at the injured or infected site produce factors to repair wounds, clot the blood, and fight any infective agents.
• In the process, the surrounding area becomes inflamed and some healthy tissue is injured.
• Under normal conditions, the immune system has other factors that control and limit this inflammatory process.

Text Continues Below

---

The Infection Fighters. The primary infection-fighting units are two types of white blood cells: lymphocytes and leukocytes.

Lymphocytes include two subtypes known as T cells and B cells. Both types of cells are designed to recognize foreign substances (antigens) and to launch an offensive or defensive action against them:

• B cells produce antibodies, which are designed to attack the antigens. Antibodies can either ride along with a B cell or travel on their own.
• T cells have special receptors attached to their surface that recognize the specific antigen.